ANAESTHESIA FOR RESPIRATORY DISEASES

Anaesthesia for Respiratory Diseases:- 

 Obstructive (asthma and COPD) or restrictive diseases are classified as Pulmonary diseases. 

GENERAL CONSIDERATIONS IN MANAGEMENT OF PATIENT WITH PULMONARY DISEASE

Preoperative Considerations

Determining  the major risk factors which dispose the patient to post- operative pulmonary problems is One of the essential  parts of preoperative evaluation .

The risk factors given below cited as the major 

Risk factors:

• Age> 60 years.

• Severity of pulmonary disease (Dyspnea at minimal activity) ASA grade > 2.

• Congestive heart failure.

• Heavy smoker.

• Surgery under general anesthesia. 

• Surgical factors like site of surgery (thoracic and upper abdominal),nature & duration (>3hrs) .

 Dyspnea at minimal activity and site of surgery are the two most important predictors of postoperative complications.

1-  Ideally smoking should be stopped 8 weeks before surgery however stopping smoking 12 hours before may be beneficial by reducing carboxyhemoglobin levels.

2- Although pulmonary / Lung function test ( PFT) do determine the severity of disease but are not always predictors of complications therefore routine use of PFT is not recommended.

3-  Patients with pulmonary diseases should be given chest physiotherapy, antibiotics, bronchodilators and steroids in preoperative period to improve their respiratory status.

4-  Patients who are on steroids at present or have taken steroid earlier should receive supplemental steroid , any infection must be treated before taking the patient for surgery.

5-  Bronchodilators should be continued as instructed; however, there is no role of prophylactic nebulization in asymptomatic patient.

 The patient should bring his/her inhalers with him/her in operation Room (OR).

Premedication: 

Premedication with benzodizepines  should be avoided as these  patients are more sensitive  to respiratory depression. Theoretically premedication along  with anticholinergic is beneficial by causing bronchodilatation, however, clinical advantage has not been seen. Premedication with H2 blockers (Ranitidine) should be avoided because H2 blockade leads to unopposed H1 activation and bronchospasm.

Intraoperative Considerations

Hypoxia, hypercarbia, acidosis and sepsis are not acceptable.

Choice of Anesthesia

Regional anesthesia is always preferred over general anesthesia. 

If the level of block required is below T6, then Central neuraxial blocks are excellent choice of anaesthesia. 

 Level above T6 can cause paralysis of abdominal muscles causing significant distress (particularly in COPD patients) because these patients have active opioids can causes respiratory depression therefore should be avoided as far as possible.

Expiration dependent on abdominal muscles. If general anesthesia is to be given following should be given due consideration:

Gases must be humidified. Dry gases can inhibit ciliary function causing atelectasis in postoperative period. Moreover, all inhalational agents (except ether) also inhibit ciliary activity.

General anesthesia increases the dead space and V/Q mismatch .

Ventilatory responses to hypoxia and hypercarbia are blunted by inhalational agents, barbiturates and opioids and this can be deleterious in a patient on spontaneous ventilation.

Ventilation principle includes low tidal volume (6-8 mL/kg) to avoid barotrauma, relevant. low E E ratio and slow respiratory rate of (6-10 breaths/min.) to allow adequate exhalation and prevent air trapping.

Postoperative Considerations

Pulmonary patients are prone to develop atelectasis and hypoxia in postoperative duration . Not only they require respiratory monitoring and supplemental oxygen but lung expansion measures (incentive spirometry, chest physiotherapy, deep breathing exercises) should also be instituted as early as possible. Ideally the improvement in pulmonary/ Lung  functions should be guided by Propofol is a reasonable bronchodilator devoid functional residual capacity (FRC).

The most important consideration is to prevent reflex stimulation of airways by laryngoscopy and most safe, most effective and most commonly used Intubation.

Pain can significantly compromise the pulmonary functions especially in thoracic and upper abdominal surgeries therefore pain management is most essential for thoracic and upper abdominal surgeries in respiratory compromised patients. 

Thoracic epidural is the most preferred,most safe,  approach to achieve analgesia for thoracic and upper abdominal surgeries. Other techniques which can be used are intercostal block, local infiltration (2 levels above and below the thoracotomy incision site),

 intrapleural analgesia and cryoanalgesia with special probes which freezes intercostal nerves. Cryoanalgesia, although produces effective pain relief, however, not used commonly due to delayed onset, nonavailability of probes and very long lasting effect nerve recovery may even take 1-6 months. 

Parenteral opioids can causes respuratory depression therefore should be avoided as far as possible. 

ASTHMA

To consider for elective surgery the patient must not have active asthma (no wheeze or rhonchi) and ideally should have 80% of predicted value of peak expiratory flow rate.

Anaesthetic Management

Choice of Anesthesia:- 

As discussed regional anesthesia is preferred over general anesthesia. Avoid central neuraxial block if the level of block required is above T6. The other concern of spinal that sympathetic block leads to parasympathetic stimulation and consequent bronchospasm has not been found to be clinically relevant. 

General Anesthesia

Induction

Ketamine in spite of its best bronchodilator property is generally avoided due to its side effect (especially vivid reactions) and propensity to increase tracheobronchial secretions. The use of ketamine nowadays  practice is restricted to patients in active asthma (wheezing) undergoing life threatening emergency surgeries. 

Ketamine in patient taking theophylline can precipitate seizures.

Propofol is a reasonable bronchodilator devoud of side effects seen with ketamine therefore, is more preferred for asthma patients in present day anesthesia practice.

 Thiopentone can induce bronchoconstriction therefore, should be avoided.

Maintenance:

 Sevoflurane is the inhalational agent of choice for asthma patients. Halothane, in spite of producing little more bronchodilatation than sevoflurane in asthma patients is not preferred because of the increase possibility of arrhythmias. As desflurane and isoflurane have irritating effects on airways therefore should be avoided.

Muscle relaxant :  Steroidal class of muscle relaxant is preferred. Benzylisoquinolines by release histamine can precipitate bronchospasm.

To avoid immediate postoperative broncho spasm extubation should be done when patient is deep (deep extubation) .

Management of Intraoperative Bronchospasm 

 Diagnosis :-

Intraoperative bronchospasm is diagnosed by

•  Wheezing

•  Increase in peak airway pressure

•  Decrease exhaled tidal volume

•  Prolonged phase II (slowly rising CO2) on            capnography

•  Decrease oxygen saturation in extreme cases.

      

Treatment:- 

Step 1: Before starting therapy for asthma it is must to rule out other causes of increased airway pressure/bronchospasm like obstruction of endotracheal tube by secretions or kinking. inadequate depth of anesthesia, pulmonary edema, aspiration or embolus, pneumothorax.

Step 2: Once it is confirmed that bronchospasm is due to asthmatic attack it should first be treated by increasing the depth of anesthesia with inhalational agent (preferably Sevoflurane).

Step 3: If not relieved by increasing the depth, inhaled B, agonist (with or without inhaled steroid) therapy should be instituted immediately.

Step 4: Still not relieved by inhaled B, agonist consider giving IV steroids, however, it should be kept in mind that the effect of steroids can take few hours.

Step 5: For refractory bronchospasm not responding to above said measures consider ephinephrine , ketamine or aminophyline infusion.

CHRONIC OBSTRUCTIVE PULMONARY DISEASE (CHRONIC BRONCHITIS AND EMPHYSEMA)

Chronic obstructive pulmonary disease (COPD) is the most common pulmonary disease encountered in clinical practice.

The anesthetic management of COPD patients  is similar to asthma patient with additional emphasis on the points given below: 

⚫ Cor pulmonale must be ruled out and if there is any evidence of pulmonary hypertension then nitrous oxide should be avoided.

⚫Patients must be stabilized by stopping smoking,treating infection,correcting spasm (asthmatic bronchitis),improve pulmonary condition by physiotherapy before taking for elective surgery. 

⚫Nitrous oxide should not be used in emphysema. It can cause expansion of bullae leading to rupture & pneumothorax. 

⚫Ventilation principle of low tidal volumes and slow respiratory rate must be adhered . 

RESTRICTIVE LUNG DISEASES

These patients have low FRC therefore are more prone for hypoxemia during induction. As these patients are very vulnerable to barotrauma avoiding large tidal volumes and inspiratory pressures is the most important principle of ventilatory management during general anesthesia (GA).

 TUBERCULOSIS : 

Elective surgery should be deferred in a patient of active (open) pulmonary tuberculosis. Pulmonary damage caused by tuberculosis should be assessed in preoperative period.

Antitubercular drugs should be continued however, assessment of liver functions is must. Emergency surgery of an active case should be performed in separate theater dedicated for infected cases. Equipment coming in direct contact with patient like mask, laryngeal mask airway (LMA), breathing circuits should be discarded after case while other equipment and theater should be sterilized properly.

RESPIRATORY TRACT INFECTION: 

Elective surgery is contraindicated in patients with lower respiratory tract infection (lung infections). The decision to go ahead with elective surgery in patient with upper respiratory tract infection (URTI) depends on the severity of the disease.

Patients with minimal URTI (viral infections), i.e. only running nose, occasional cough without expectoration and afebrile can go ahead with elective surgery however if the patient has significant URTI, i.e. significant cough or cough with expectoration, fever, signs of lower upper airway o surgery should ideally be deferred for 6 weeks.

As airway remains hyperactive for 5-6 weeks after a significant URTI, deferring surgery for less than 6 weeks does not solve the purpose, therefore if surgery has to postponed then it should be deferred for 6 weeks otherwise take the patient with calculated risks; the incidence of respiratory complications in acute phase and recovery phase remains same.

Patients undergoing surgery with active URTI are prone to develop complications like laryngospasm (5 times), bronchospasm (10 times). hypoxia, increased bleeding from airways, post Intubation croup, lower respiratory tract infection (infection may spread to lower respiratory tract by intubation leading to pneumonitis, atelectasis or even septicemia).

To avoid these complications the following approach should be used in patients with active URTI undergoing surgery: 

• Anesthesia of choice is regional.

• If GA is to be given then prefer to get the surgery done under laryngeal mask airway  Avoid intubation as far as possible,however, if intubation is necessary then reflex stimulation of airways by laryngoscopy and intubation should be prevented.

• Use of anticholinergic is strongly recommended.

• Humidification of gases is must.

• Be ready for cricothyroidotomy and/or         tracheostomy should there occur significant   upper airway obstruction. 

• Keep the patients for longer periods in post operative room for respiratory monitoring.

OPERATIVE CRITERIA FOR THORACOTOMY/PNEUMONECTOMY

The pulmonary pathology to the following extent usually requires surgical correction by thoracotomy/pneumonectomy.

• FEVI <2 liters

• FEV1/FVC ratio <50% of predicted.

• Maximum breathing capacity <50% of predicted.

• PCO,>45 and PO,<50 mm Hg at room air.

• Oxygen consumption <10ml/kg/min. 

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